U.S. Pat. No. 3,056,638 for a reciprocating engine creates a recurring small gap below the piston pin to renew the oil film. It discloses a piston-and-connecting rod assembly. The upper end (the “small end”) of the connecting rod is shaped not round but slightly eccentric to the axis of the piston pin. Once per crankshaft revolution, the eccentric meshes with a concave surface under the piston crown. This is caused by the natural oscillation of the connecting rod as its angularity changes continually during crankshaft rotation. The bulging portion of the eccentric acts as a cam when it passes under the concave surface, pushing up on it. The piston moves up slightly, as do the piston pin bosses. They pull the piston pin upward a little, creating increased clearance to the bushing in the rod small end. A renewal oil film can penetrate the increased clearance between the bottom of the pin and the bottom of the bushing. This restores the oil film between the piston pin and the bushing.
Our invention also unloads the piston pin, but the implementation is different. Hydraulic pressure is used to push upward on the bottom of the piston crown. The result is also different: The clearance obtained is between the piston pin and the piston pin bosses.
U.S. Pat. No. 3,027,207 will achieve the same result, but mechanically. The action is almost identical to that of U.S. Pat. No. 3,056,638 above. Clearance for a renewal oil film was not claimed, however, because his intent was direct bearing of the piston head on the connecting rod.
U.S. Pat. No. 3,200,798 for a variable compression ratio piston has an oil pumping action somewhat close to our own. A raised bump on the connecting rod small end pushes on a pump plunger. Pressurized oil is sent upward into a chamber under the moveable piston crown, causing it to lift. Quite similar to our mechanism. But his raised bump works as a cam, which is subject to wear. The push on our plunger is aligned with the back of the plunger.
In U.S. Pat. No. 2,066,489 the wear limitation is decreased by an arm pushing on the pump plunger. However, most of the contact includes sliding. An improvement is the arm shaped as a gear tooth. This has rolling contact at the pitch radius of mesh, a likely place for the point of highest load, therefore a good thing. But sliding wear remains at the other points.